Caster

ABSTRACT

A caster which is mounted in a trolley or the like having a bracket  2  connected to a body of a vehicle; a link  3  connected to rotate on the bracket  2;  vehicle wheels  4  connected to rotate on the link  3;  and a compressible rubber block  20  which deforms as the link  3  rotates. The compressible rubber block forms an initial compressible part  23  which partially eliminates a surface area of the compressible rubber block. In this manner it is possible to restrain input forces on the vehicle body by smoothing out the rotation of the link  3.

FIELD OF THE INVENTION

This invention relates to a caster which is provided with a dampingmechanism and which is mounted on a wheelchair or the like.

BACKGROUND OF THE INVENTION

A prior art caster for absorbing shocks comprises a bracket which isconnected to a body, a link which is connected to rotate with thebracket and which supports a wheel, and a cushioning which is interposedbetween the bracket and the link.

DISCLOSURE OF THE INVENTION

However the carrying load and shock-absorbing efficiency of this type ofcaster are determined by the resilient characteristics of the cushioningrubber. As a result, the problem has arisen that the effectiveness of aninitial movement is reduced if the cushioning rubber is too hard.Conversely metal contact may result if the cushioning rubber is toosoft.

The caster is provided with a metal spring has resulted in the problemthat the size of the caster is increased and thus it is difficult toassemble this type of caster into the wheelchair currently in use.

This invention has the object of providing a caster which solves theabove problems.

In order to solve the above problems, this invention provides a castercomprising a bracket which is connected with a body of a vehicle, a linkwhich is connected with the bracket rotatably, a wheel which isconnected with the link rotatably, and a compressible rubber block whichdeforms according to the rotation of the link, wherein the compressiblerubber block has an initial compressible part which partially decreasesa cross section of the compressible rubber block. As a result, thecompressible rubber block can smooth out the rotation of the link andrestrain input forces on the body by the initial compressible partdeforming with respect to an initial input force on the wheels.

When a large input force is applied on the wheels, the input force onthe body is restrained by limiting the rotation range of the link whichthus prevents metal contact comprising the link making direct contactwith the bracket etc. This is enabled by the deformation of sectionsother than the initial compressible part after the initial compressiblepart has deformed.

A torsional rubber bush is disposed co-axially to the rotational axis ofthe link and a compressible rubber block is disposed between the bracketand the link. As a result, the size of the caster can be made reduced.

The initial compressible rubber block is made a cylindrical shape and apart of the cylindrical compressible rubber block is formed a cone shapewhich has a reduced cross section. As a result, when the compressiblerubber block is compressed, deformation begins from the initialcompressible part which has a smaller cross section. Thereafter theelastic recovery force rapidly increases due to the fact that conicalparts deform from the side which has the smaller cross section togetherwith increases in the degree of deformation. The conical parts arepositioned to sandwich the initial compressible part.

The compressible rubber block has a cylindrical shape and at least apart of the cylindrical compressible rubber block as the initialcompressible part is formed so that a cross section of the part issmaller than other parts. As a result, when the compressible rubberblock is compressed, firstly deformation begins from the initialcompressible part which has a smaller cross section. Thereafter theelastic recovering force rapidly increases due to the fact that eachlarge diameter part which sandwiches the initial compressible partundergoes deformation. In this manner, shocks on the wheel from the roadsurface are effectively absorbed and input forces on the body can berestrained by preventing metal contact resulting from the link cominginto contact with the bracket.

A retainer is provided at periphery of the compressible rubber block,and the retainer come into contact with a member supporting thecompressible rubber block according to the deformation of the initialcompressible part. As a result, when the compressible rubber block iscompressed, it is compressed firstly from the initial compressible partwhich has a smaller cross section and the retainer abuts with the amember which supports the initial compressible part. As a result, theelastic recovering force is rapidly increased. In this manner, shocks onthe wheel from the road surface are effectively absorbed and inputforces to the vehicle body can be restrained by preventing metal contactdue to the link coming into contact with the bracket.

Annular spacers are respectively provided at the top side and bottomside of the compressible rubber block, a maximum amount of compressionof the compressible rubber block is determined by which the respectivespacers contacts as the deformation of the compressible rubber block.Therefore the compression ratio of the compressible rubber block can belimited by the contact between the spacers. Therefore it is possible toaccurately control the amount of stroke of the casters and thereforerestrain individual differences in damping performance resulting fromdifferences quality in the manufacture of the compressible rubberblocks.

The annular spacer has a height regulation member which enables amaximum amount of compression of the compressible rubber block to bevaried. Therefore it is possible to vary the amount of stroke of thecaster in a simple manner.

The cross section of the initial compressible rubber block is graduallydecreased toward a top of the compressible rubber block to a deformationdirection of the compressible rubber block, annular spacers arerespectively provided at the top side and bottom side of thecompressible rubber block and the respective spacers contacts with theinitial compressible rubber block according to the deformation of thecompressible rubber block. Therefore as the initial compressible sectionis compressed, the end of the block abuts with the end face of thespacer. As a result, when the compressible rubber block is compressed,deformation begins from the initial compressible part which has asmaller surface area. Therefore the input forces on the vehicle body canbe restrained by smoothing out the rotation of the link. When a largeinput force is applied to the vehicle wheels, the initial compressiblepart of the compressible rubber block comes into contact with the endface of the spacer. Therefore the elastic recovering force of thecompressible rubber block increases sharply. As a result, it is possibleto restrain input forces on the vehicle body by limiting the rotationrange of the link.

A torsional rubber bush as the compressible rubber block is providedwhich deforms to a torsion direction as the link rotates As a result,the torsional rubber cushion forms a torsion in response to loads on thevehicle body to determine the inclination of the link. The compressiblerubber block is compressed in response to input forces on the vehiclewheels and swing in the link is damped. Thus it is possible to set theload bearing characteristics and damping characteristics of the casteron the basis of variations in the hardness or shape of the torsionalrubber bush and the compressible rubber block.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a caster according to a first embodiment ofthis invention.

FIG. 2 is a front view of a caster according to a first embodiment ofthis invention.

FIG. 3 is a side view of a compressible rubber block according to afirst embodiment of this invention.

FIG. 4 shows the characteristics of the relationship of amount ofdisplacement of the compressible rubber block and the resilient load onthe compressible rubber block according to a first embodiment.

FIG. 5 is a side view of a compressible rubber block according to asecond embodiment of this invention.

FIG. 6 is a side view of a compressible rubber block according to athird embodiment of this invention.

FIG. 7 shows the characteristics of the relationship of amount ofdisplacement of the compressible rubber block and a resilient load onthe compressible rubber block.

FIG. 8 is a side view of a caster according to a fourth embodiment ofthis invention.

FIG. 9 is a front view of a caster according to a fourth embodiment ofthis invention.

FIG. 10 is a sectional view of a compressible rubber block according toa fourth embodiment of this invention.

FIG. 11 is a sectional view of a compressible rubber block according toa fifth embodiment of this invention.

FIG. 12 is a sectional view of a compressible rubber block according toa sixth embodiment of this invention.

FIG. 13 shows the characteristics of the relationship of amount ofdisplacement of the link and the resilient load on the compressiblerubber block according to a sixth embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to describe the invention in greater detail, the preferredembodiments will be outlined below with reference to the accompanyingfigures.

Referring to FIG. 1 of the drawings, a caster 1 comprises a bracket 2which is fixed to a body for example of a wheelchair, a link 3 which issupported to rotate on the bracket 2 and a wheel 4 which is supported torotate on a front end of the link 3.

The bracket 2 is U-shaped in cross section and is fixed to the vehiclebody by a bolt 5 which pierces an upper end of the bracket 2.Alternatively the bracket 2 may be connected to the body through abearing, the link 3 may be adapted to swing about a perpendicular axis(transverse direction) in the direction in which the wheels 4 aremoving.

The link 3 is U-shaped in cross section and a bolt 6 is provided whichpierces a front end of the link 3. The bolt 6 supports the wheels 4 torotate through a bearing (not shown).

As shown in FIG. 2, the link 3 is supported to rotate horizontally(vertical direction) with respect to the bracket 2 through a torsionalrubber bush 10 which comprises a rubber material. An outer sleeve 13 andan inner sleeve 11 are fixed by vulcanization to inner and outerperipheral faces of the cylindrical torsional rubber bush 10. Thetorsional rubber bush 10 is press fitted to a sleeve 12 which isprovided on a rotational center of the link 3. On the other hand, theinner sleeve 11 is fixed to the bracket 2 by a bolt 7.

Under design standards, the torsional rubber bush 10 is attached so thatduring a torsional deformation, its inner and outer peripheral facesboth undergo relative displacement in a peripheral direction. Thetorsional rubber bush 10 rotates the link 3 downwardly with the elasticrecovering force. A torsional deformation is generated in the torsionalrubber bush 10 in response to the load on the body which thus determinesthe inclination of the link 3 to a horizontal line. When the link 3makes contact with a stopper bolt 9 which is described below, thetorsional rubber bush 10 may be set not to generate a torsionaldeformation.

A pair of stopper bolts 9 are fixed to the bracket 2 to limit downwardrotation of the link 3. When a load is not applied to the caster 1,contact of the link 3 with each stopper bolt 9 is maintained by theelastic recovering force of the torsional rubber bush 10.

A compressible rubber block 20 is mounted on the bracket 2 which iscompressed by the upward rotation of the link 3. Swing of the link 3 isrestrained by the link 3 rotating as the compressible rubber block 20 iscompressed in response to an input force on the wheels 4 from the roadsurface. Furthermore metal contact resulting from the wheels 4contacting the bracket 2 or the vehicle body is prevented.

An annular spacer 15 is fixed to the bracket 2 and an upper part of thecompressible rubber block 20 is retained in an inner side of the spacer15.

An annular spacer 16 is fixed to the link 3 and a lower part of thecompressible rubber block 20 is retained in an inner side of the spacer16.

As shown in FIG. 3, the compressible rubber block 20 which comprises arubber material has an initial compressible part 23 which partiallyeliminates the cross section of the block 20. The increase ratio inloads applied to the link 3 gradually increases in response to theamount of compression.

In this embodiment, the shape of the compressible rubber block 20 ismade by connecting a respective top surface of two truncated cones, theinitial compressible part 23 means connecting surface of two topsurface. That is to say, the compressible rubber block 20 has aninverted truncated cone 22 in which the cross sectional area decreasesfrom an upper part 21 to a central part and a truncated cone 24 in whichthe cross sectional area decreases from a lower part 25 to a centralpart. The initial compressible part 23 is formed between the invertedtruncated cone 22 and the truncated cone 24.

When the compressible rubber block 20 is compressed, it deforms firstlyfrom the initial compressible part 23 which has a smaller cross section.The inverted truncated cone 22 and the truncated cone 24 which sandwichthe initial compressible part 23 deform together with increases in theamount of compression. In this manner, the elastic recovery force whichis applied by the compressible rubber block 20 rapidly increases. FIG. 4shows the characteristics of the relationship of the displacement of thelink 3 (the amount of compression of the compressible rubber block 20)and a resilient load compressing the compressible rubber block 20pressing the link 3 downwardly. The increase ratio in the resilient loadof the compressible rubber block 20 displays non-linear characteristicsand gradually increases as the displacement of the link 3 increases. InFIG. 4, the characteristics of the caster provided with the cylindricalcompressible rubber block are shown by the broken line. In this case,the increase ratio in the resilient load of the compressible rubberblock 20 is approximately fixed with respect to the amount ofdisplacement of the link.

The inclination of the link 3 is determined by the torsional deformationof the torsional rubber bush 10 in response to loads applied to the body. The link 3 comes into contact with the compressible rubber block 20 inresponse to an input force on the wheel 4. The compressible rubber block20 is compressed by such contact and the swinging of the link 3 isdamped. Thus it is possible to set a permissible load and dampingcharacteristics of the caster 1 by varying the respective rubberhardness and shape of the rubber of the compressible rubber block 20 andthe torsional rubber bush 10.

The compressible rubber block 20 restrains input forces on the body fromthe link 3 due to the deformation of the initial compressible part 23with respect to initial input forces on the wheel 4. And with respect tolarge input forces on the vehicle wheel 4, the compressible rubber block20 deforms sections other than the initial compressible part 23. In thismanner, metal contact is prevented by limiting the rotation range of thelink 3 and input forces on the body are restrained by effective shockabsorption.

A second embodiment of this invention will be described below withreference to FIG. 5. A cylindrical compressible rubber block 30 hasinitial compressible parts 32, 34 at two parts along the compressiblerubber block 30 which are formed in an annular shape and have anapproximately rectangular-shaped cross section. Furthermore three largediameter parts 31, 33, 35 are provided as to sandwich each initialcompressible part 32, 34.

When the compressible rubber block 30 is compressed, the deformation ofthe block 30 begins firstly from each initial compressible part 32, 34which has a smaller cross section. After the deformation the initialcompressible part 32, 34, large diameter part 31, 33, 35 whichsandwiches each initial compressible part 32, 33 begins the deformationand the elastic recovery force which is applied by the compressiblerubber block 30 increases rapidly. In this manner, it is possible toabsorb effectively the shock to the wheels from the road surface and todecrease the input forces on the body by preventing metal contactbetween the link 3 and the bracket 2.

A torsional rubber bush 10 is disposed co-axially to the rotational axisof the link 3 and a compressible rubber block 30 is disposed between thebracket 2 and the link 3. As a result, the size of the caster 1 can bereduced.

A third embodiment as shown in FIG. 6 will be described below. Acompressible rubber block 40 is provided with a cylindrical initialcompressible part 41, a cylindrical part 42 and a disk-shaped metallicretainer 43. The cylindrical initial compressible part 41 is interposedacross the bracket 2 and the link 3. The cylindrical part 42 is disposedon the outer periphery of the initial compressible part 41. Thedisk-shaped metallic retainer 43 is disposed on the outer periphery ofthe initial compressible part 41 and arranged on the upper face of thecylindrical part 42.

An upper part of the initial compressible part 41 is engaged with aspacer 15 of the bracket 2 and a lower part is engaged to a spacer 16 ofthe link 3 through the cylindrical part 42.

When the compressible rubber block 40 is compressed, the deformationbegins firstly from the initial compressible part 41 which has a smallercross section. After this deformation, the cylindrical part 42 iscompressed according to the contact between the retainer 43 and thespacer 15 of the bracket 2. In this manner, as shown in FIG. 7, theelastic recovery force applied by the compressible rubber block 40increases rapidly. Thus it is possible to absorb effectively the shockto the wheel from the road surface and to decrease the input forces onthe body by preventing metal contact between the link 3 and the bracket2.

A fourth embodiment is shown in FIG. 8 and FIG. 9. Those componentscommon to the above embodiments described above are denoted by the samereference numerals.

As shown by FIG. 8, the caster 1 comprises a bracket 2 fixed to the bodyof a trolley for instance, a link 3 supported as to rotate on thebracket 2 and wheel 4 supported as to rotate on the front end of thelink 3.

The wheel 4 is supported through a bolt 6 as to rotate on a front end ofthe link 3. Although the wheel 4 shown in the figure has a radius of 5inches, a bolt hole 49 which supports the wheel with a 6 inch radius isformed on the front end of the link 3.

The bracket 2 has a U-shaped cross section and is connected to rotate onthe body through bearings 51, 52 by a bolt 53 which passes through anupper section of the bracket 2. The link 3 rotates around a verticalaxis (in a transverse direction). The wheel 4 turns to a travelingdirection.

As shown in FIG. 9, the link 3 has a U-shaped cross section and isconnected to rotate on the bracket 2 through a pin 54 which passesthrough the rotational center of the link 3. A sleeve 55 is fixedco-axially to the rotational center of the link 3 and the sleeve 55 isengaged slidably on the pin 54.

A pair of stopper bolts 9 are engaged to the bracket 2 to limit therotation of the link 3 in a downward direction.

A compressible rubber block 60 is mounted to the bracket 2 as to becompressed according to the upward rotation of the link 3. Thecompressible rubber block 60 begins the compression deformation inresponse to loads on the body and the inclination of the link 3 isdetermined by an amount of this deformation. The link 3 rotates as thecompressible rubber block 60 is compressed in response to input forceson the wheel 4 from the road surface. In this manner, swinging of thelink 3 is restrained and metallic contact is prevented between the link3 or the wheel 4 and the bracket 2.

As shown in FIG. 10, the cylindrical compressible rubber block 60comprises a cylindrical upper part 61, a cylindrical lower part 63 andan initial compressible part 62 formed in a conical shape from the lowerpart 63 to the upper part 61.

An annular spacer 46 is fixed to the link 3 and a lower part 64 of thecompressible rubber block 60 is supported on an inner side of the spacer46.

An annular spacer 45 is fixed to the bracket 2 and the upper part 61 ofthe compressible rubber block 60 is supported on an inner side of thespacer 45.

When the compressible rubber block 60 is compressed, it deforms firstlyfrom the initial compressible part 62 which has a smaller cross section.The initial compressible part 62 contacts the lower face 48 of anannular fixing seat 45 in response to increases in the amount ofcompression. The elastic recovery force applied by the compressiblerubber block 60 increases rapidly and thus the increase ratio in loadson the link 3 which correspond to the amount of compression graduallyincreases in response to the amount of compression.

A compressible rubber block 60 arranged as above is compressed inresponse to loads on the body and the inclination of the link 3 isdetermined by this deformation. The compressible rubber block 60 isfurther compressed in response to the input forces on the wheel 4 as theresult the swinging of the link 3 is damped. Thus it is possible to setdamping characteristics and the load characteristics of the caster 1 onthe basis of variations in the rubber hardness and shape of thecompressible rubber block 60.

The compressible rubber block 60 smoothes out the rotation of the link 3and restrains input forces on the body by deforming the initialcompressible part 62 with respect to initial input forces on the wheel4. And with respect to larger input forces on the wheel, in addition tothe initial compressible part 62 of the compressible rubber block 60,the other parts 61, 63 begin to deform. Therefore a resilient recoveryforce applied by the compressible rubber block 60 increases rapidly.Metal contact can be prevented by limiting the rotation range of thelink 3 and input forces on the body can be restrained by effective shockabsorption.

Referring to FIG. 11, a fifth embodiment will be explained. Thisdetermines the compression ratio of a compressible rubber block 74 bycontact between a stopper ring 70 and the spacer 45.

The stopper ring 70 limits the compression ratio of the compressiblerubber block 74 and a ring 71 which comes into contact a spacer 45. Thatis to say, the stopper ring 70 comprises a shim 72 which limits thelength between the spacer 45 and the ring 71, and a case 73 which housesthe ring 71 and the shim 72.

The inner radius of the ring 71 and the shim 72 is greater than theouter radius of the compressible rubber block 74. The volume of thespace which is between the inner radius of the ring 71 and the shim 72,and the outer radius of the compressible rubber block 74 is maintainedat a greater value than the rubber volume of the amount of deformationwhen the compressible rubber block 74 is compressed to a maximum (thatis to say, when the spacer 45 and the ring 71 are in contact).

The above arrangement allows the compression ratio of the compressiblerubber block 74 to be limited by the contact of the spacer 45 and thering 71. Thus it is possible to control the stroke amount of the casteraccurately and to restrain individual differences in the dampingperformance resulting from quality difference in the manufacture of thecompressible rubber block 74.

Thus it is possible to vary the compression ratio of the compressiblerubber block 74, that is to say, to vary the stroke amount of the casterwith an extremely simple manner by suitably regulating the number ofshims 72.

A sixth embodiment will be described with reference to FIG. 12 whichrepresents a variation on the shape of the compressible rubber block 60shown in FIG. 10.

A compressible rubber block 80 in this embodiment comprises acylindrical upper part 81 which has a smaller diameter, a cylindricallower part 83 which has a bigger diameter and a tapering compressiblepart 82 which fastens the upper part 81 and the lower part 83. The ratioof the length of the upper part 81 with respect to the overall length ofthe compressible rubber block 80 is lengthened in this embodiment incomparison with the fourth embodiment shown in FIG. 10. That is to say,the upper part 81 is lengthened.

In the above structure, when a load is applied to the compressiblerubber block 80, firstly the upper part 81 which has the smaller crosssection begins to deform, and then the compressible part 82 and thelower part 83 deform in that order. When this is expressed as load anddeformation characteristics of the compressible rubber block, theinitial compressible part 62 of the compressible rubber block 60 of thefourth embodiment as shown in FIG. 13 begins to deform as soon as a loadis applied. However due to having a conical shape, the initialcompressible part 62 immediately displays non-linear deformationcharacteristics. In contrast, the present embodiment displays linearcharacteristics up to a fixed amount of deformation since the upper part81 which has a fixed cross section deforms first. Thereafter, thepresent embodiment also displays non-linear characteristics as shown inFIG. 13 which are attributable to the characteristics of thecompressible part 82 and the lower part 83.

Thus the above structure makes it is possible to soften initialresilient characteristics when a load is applied. This makes it possibleto improve the comfort of a trolley or in particular a wheelchair.

Each embodiment for a caster above is not limited to a vehicle whichcarries goods and may also be used on a wheelchair for example.

Industrial Application

As shown above, the caster according to the present invention restrainsinput forces on the body by smoothing out the rotation of a link. Thisis enabled by providing an initial compressible part for a compressiblerubber block which deforms with respect to an initial input forceapplied on wheel. Furthermore sections other than the initialcompressible part deform with respect to large input forces on thewheel. In this manner, by limiting the rotational range of the link,metallic contact due to shocks on the bracket is prevented. Thereforethe caster may be applied to trolleys or more particularly towheelchairs.

What is claimed is:
 1. A caster, comprising: a bracket which isconnectable with a body of a vehicle; a link having a first end which isrotatably connected with the bracket; a wheel which is rotatablyconnected with a second end of the link; a torsional rubber bushdisposed at the first end of the link and which torsionally deforms asthe link rotates; and a compressible rubber block disposed at the secondend of the link and which deforms according to the rotation of the link,the compressible rubber block having an initial compressible part whichhas a decreased cross section relative to a remainder of thecompressible rubber block, said torsional rubber bush and saidcompressible rubber block cooperating together to set a permissible loadand damping characteristics of said caster.
 2. The caster as defined inclaim 1, wherein the compressible rubber block has a cone shape partwhich forms the initially compressible part having the decreased crosssection.
 3. The caster as defined in claim 1, wherein the compressiblerubber block has a cylindrical shape having a first diameter, at leastthe initial compressible part having a second diameter that is less thanthe first diameter.
 4. The caster as defined in claim 1, furthercomprising a retainer provided at a periphery of the compressible rubberblock, the retainer coming into contact with a member supporting thecompressible rubber block according to a deformation of the initialcompressible part.
 5. The caster as defined in claim 1, furthercomprising annular spacers respectively provided at a top side and abottom side of the compressible rubber block, a maximum amount ofcompression of the compressible rubber block being determined by aninitial contact between the respective spacers as the compressiblerubber block is deformed.
 6. The caster as defined in claim 5, whereinthe annular spacer at the bottom side of the compressible rubber blockhas a height regulation member which enables a maximum amount ofcompression of the compressible rubber block to be varied.
 7. The casteras defined in claim 1, wherein the cross section of the compressiblerubber block is gradually decreased toward a top of the compressiblerubber block in a deformation direction of the compressible rubberblock; further comprising annular spacers respectively provided at a topside and a bottom side of the compressible rubber block, the respectivespacers contacting with the compressible rubber block according to adeformation of the compressible rubber block.
 8. The caster as definedin claim 2, further comprising annular spacers respectively provided ata top side and a bottom side of the compressible rubber block, a maximumamount of compression of the compressible rubber block being determinedby an initial contact between the respective spacers as the compressiblerubber block is deformed.
 9. The caster as defined in claim 3, furthercomprising annular spacers respectively provided at a top side and abottom side of the compressible rubber block, a maximum amount ofcompression of the compressible rubber block being determined by aninitial contact between the respective spacers as the compressiblerubber block is deformed.
 10. The caster as defined in claim 4, furthercomprising annular spacers respectively provided at a top side and abottom side of the compressible rubber block, a maximum amount ofcompression of the compressible rubber block being determined by aninitial contact between the respective spacers as the compressiblerubber block is deformed.